Tainted Suns
Imagine if the outer atmosphere of the sun could be tainted with a particular ion that acts like a switch for a particular bandwidth, rapidly changing the opacity, or other other optical property, when stimulated by outside laser scanning. An orbiting laser platform scans the entire surface of the sun, toggling the ion between two different states. The suns light is affected differently in each state, massively amplifying a digital signal, detectable at intergalactic distances! That'd be cool.